1. Field of the Invention
The present invention relates to a liquid jet apparatus for ejecting liquid drops from nozzle openings formed on a liquid jet head and a cleaning method for the liquid jet head of the liquid jet apparatus.
2. Description of the Related Art
As a typical example of a conventional liquid jet apparatus, there is an ink jet recording apparatus having an ink jet recording head for image recording. As other liquid jet apparatus, for example, an apparatus having a color material jet head used for manufacturing color filters of a liquid crystal display, an apparatus having an electrode material (conductive paste) jet head used for forming electrodes of an organic EL or an FED (face emission display), an apparatus having a biological organic substance jet head used for manufacturing biological chips, and an apparatus having a sample jet head as a precise pipette may be cited.
An ink jet recording apparatus as a typical example of a liquid jet apparatus makes comparatively small noise during printing and moreover can form small dots in high density, so that it has been used recently in various types of printing including color printing.
Such an ink jet recording apparatus generally has an ink jet recording head (liquid jet head) which is loaded on a carriage and moves back and forth in the width direction (head scanning direction) of a recording medium such as recording paper and a feed means for moving the recording medium in the direction (medium feed direction) perpendicular to the head scanning direction.
In the ink jet recording apparatus, printing is executed by ejecting ink drops (liquid drops) from the recording head to the recording medium in correspondence with print data. And, the recording head loaded on the carriage is structured so as to eject various colors of ink, for example, black, yellow, cyan, and magenta, thus not only text printing by black ink but also full color printing can be executed by changing the ejection rate of each ink.
Since the aforementioned recording head prints by ejecting ink pressurized in a pressure chamber as ink drops from the nozzle opening toward the recording medium, a problem arises that for example, by increasing of the ink viscosity caused by evaporation of a solvent from the nozzle opening, setting of ink, attachment of dust, moreover inclusion of air bubbles, defective printing is caused.
Therefore, when the nozzle opening of the recording head is clogged or when an ink cartridge is exchanged, the nozzle opening forming face of the recording head is sealed by the capping unit, and ink is sucked and ejected from the nozzle opening by negative pressure from a suction pump (tube pump), thus, generally, the ink jet recording apparatus is provided with a function for executing a cleaning operation for dissolving defective ink ejection due to clogging by ink setting in the nozzle opening or inclusion of air bubbles into the ink feed path.
When the cleaning operation is to be executed, for example, it is effective to generate fast ink flow if possible in the ink flow path from the ink cartridge to the nozzle opening of the recording head and by doing this, together with increased viscosity ink, air bubbles existing in the flow path can be ejected.
However, to increase the flow speed of ink in the cleaning operation, it is necessary to increase the capacity of the suction pump in order to obtain large negative pressure. For that purpose, not only a large-scale pump but also a large-scale motor for driving the pump must be used and an increase in cost and enlargement of the apparatus are unavoidable.
Furthermore, a large amount of ink is ejected from the recording head, so that the life span of the ink cartridge is shortened and a problem arises that it results in an inevitable increase in running cost for a user.
Accordingly, a recording apparatus structured so as to arrange a valve unit capable of opening and closing in the ink feed path from the ink cartridge to the recording head, during the cleaning operation, put the valve unit into the valve closed state, apply negative pressure into the capping unit, at the point of time when the negative pressure in the capping unit increases, open the valve of the valve unit, thereby instantaneously increase the ink flow speed in the recording head is proposed (for example, Japanese Patent Laid-Open Publication No. 101764/1999).
According to the constitution of this conventional proposal, it is considered that without providing a particular suction pump for obtaining large negative pressure, in the neighborhood of the nozzle opening of the recording head, set or increased viscosity ink can be ejected comparatively easily. And, the suction action is performed instantaneously from the nozzle opening, so that it is considered that as a result, the cleaning effect can be produced by ejection of a comparatively small amount of ink.
Further, International Patent Publication WO 01/53103 discloses a method for selectively executing cleaning for the black ink flow path in consideration of that the recovery of black ink during cleaning is lower than that of the other colors of ink.
However, when only the ink feed path of a specific kind of ink is selectively cleaned using the cleaning method for the ink jet recording apparatus and recording head of the aforementioned conventional proposal, there is a possibility that the meniscus of the nozzle opening for a kind of ink not to be cleaned is adversely affected. Namely, even in the nozzle opening for a kind of ink not to be selected, changing of the pressure in the capping unit acts on the meniscus, thus there is the possibility that the meniscus of the non-selected nozzle opening is destroyed by the pressure change.